1. Field of the Invention
The present invention relates to a quality control method for a production line which automatically carries out quality control of the line, which can be applied to various types of production lines such as lines for color-cathode ray tubes and semiconductor devices, and an apparatus used for the method, as well as an automatic quality control program.
2. Description of the Related Art
Production lines are designed for various types of products such as color cathode ray tubes and semiconductor devices. In the production lines, the quality of the products is controlled while they are produced.
In quality control, first, data indicating the quality of part of the products out of a great number produced on the line is sampled. The product quality data includes the results of tests carried out on products in accordance with their type, for example, the results of performance tests of the product or the results of the examination of the appearance.
Next, the overall distribution and the degree of dispersion of the sampling data are obtained. Then, the relationship between the production condition for a product and the product quality is grasped from the overall distribution and the degree of dispersion. Thus, from the relationship between the production condition and the product quality, the quality of the product is controlled.
In the quality control of a product, there is a method in which detailed examination data of the product is sampled, and defect analysis of the product is carried out by using this sampling data.
However, in many cases, the just-mentioned quality control method can only be performed by operators highly skilled in manipulation, adjustment and operation of the production line. That is, operators, who have extensive and long-term experience regarding the product and production on the production line, lean an empirical rule specially for operating the production line and have obtained skills for improving the production line.
At present, the technology for monitoring network databases, etc. has been developed, and therefore the quality management of the product is conducted on the basis of the database. In quality control, identification data such as a bar code is assigned to each and every one of the products conveyed on the production line, and the production condition data and the quality data of each and every product is stored. In this manner, quality control of the individual products can be relatively easily achieved.
In product quality control, if a great amount of data (production history data) such as production conditions and product quality of a great number of products produced is utilized effectively, it is considered possible to achieve more precise control over the quality.
However, there is a certain limit to the data processing ability of human being. Further, in the defect analysis of the products on the basis of the detailed data, the gauge of the analysis, in many cases, depends on the judgment and/or intuition of the operator who has a special empirical rule and an improving skill, and therefore the effective application of the data is further interrupted.
To summarize, with the quality control method for products, which conventionally much depends on the human factors, it is difficult to control the quality of the products by effectively making a full use of a huge amount of product history data of a great number of products.
Under the circumstances, the object of the present invention is to provide an automatic quality control method for a production line, which can effectively make a full use of a huge amount of data by overcoming the limits of the data processing capabilities of human systems or the ambiguities innate to empirical and intuitive methods of humans, and the apparatus therefor, as well as an automatic quality control program.